[29.05] The Secular Evolution of Disk-Planet and Ring-Satellite Systems

J. M. Hahn (LPI), E. Gallo (Harvard)

We are investigating the secular evolution of planetary and
satellite systems as they interact with a particle disk
having some mass. We consider two distinct systems: (i.) the
giant planets as they orbit interior to a massive primordial
Kuiper Belt, and (ii.) Saturn's rings and satellites. We
apply the low-order analytic solution of Brouwer and
Clemence (1961) to obtain the secular evolution of the
planets/satellites and the low-mass disk particles. When
applied to a primordial Kuiper Belt that is assumed to have
a mass of a few tens of Earth masses, we find that the giant
planets launch a long wavelength disturbance of dimension
\lambda ~10 AU that propagates back and forth across
this friction-free disk. This wave propagation results in
very mild excitation of the Kuiper Belt that spans its
entire width. This evolution is quite distinct from that
seen in a massless Kuiper Belt which experiences only
localized orbital excitation at secular resonances.

When this model is applied to Saturn's satellites and rings
(whose masses conform with current estimates), we see no
signs of comparable wave action. Ring gravity does not
appear to have any obvious role in the secular evolution of
this system, but we are still looking for possible subtle
influences. Instead, the rings behave the same as massless
particles that adopt the forced motions imposed by the
satellites. We find that the main rings' longitudes of
periapse \tilde{\omega} and ascending node \Omega stay
coherent over time, and this allows the A and B rings to
precess as two independent and somewhat rigid bodies under
the influence of various satellites. Curiously, the break in
the A and B rings' precession rates occurs right in the
Cassini Division, and we are investigating whether this is
an accidental coincidence or due to some cause and effect.

This research was supported by NASA Origins grant
NAG5-10946.

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